The present invention relates in general to electroluminescent display devices, and more particularly, an improved sub-pixel structure device resulting in higher efficiencies, higher yields, larger display size capabilities, and simpler manufacturing methods.
Existing electroluminescent display structures, are limited in size due to the high resistivity of the patterned transparent column conductors which creates excessive voltage drops and power losses as greater line lengths and/or higher resolutions are sought. These high resistances further limit device size by adding to the (RC) time constant of the display elements, thereby complicating various existing voltage drive methods. A method currently under development to alleviate these problems adds an active matrix behind each display element which essentially removes size limits and allows separation of the addressing voltage and frequency from the phosphor exciting voltage and frequency, hence offering higher brightness and efficiency. In order to accomplish an active matrix in electroluminescent display devices, the active transistor elements behind each pixel must be high voltage devices and the number of required high voltage devices is the product of the number of columns and rows. This compares unfavorably to the number of high voltage devices in existing passive drive methods where the total equals the sum of number of columns and rows.
It is, therefore, an object of the present invention to obviate the disadvantages of prior art by reducing electrode power losses. A further object of the present invention is to reduce the electrical time constant of existing electroluminescent devices. Still other objects of the present invention are balanced material interfaces thereby minimizing retained image phenomenon, larger size display design configurations, and a reverse construction to allow electrode structure to be completely fabricated and tested for conformity to specifications prior to adding the light emitting layer.
In general, in one aspect, the invention features an electroluminescent display device having a light emitting layer, the light emitting layer featuring a first and a second surface on opposites sides of the layer, an electrode assembly in contact with and on the first surface of the light emitting layer and a transparent conductive layer in contact with the second surface and on a side of the light emitting layer opposite from the electrode assembly.
Implementations of the invention include one or more of the following. The electrode assembly features a combination of a plurality of line patterned row and column electrodes with a plurality of sub-pixel row electrodes. The row and column line patterned electrodes are separated by a first insulating layer. The sub-pixel row electrodes are adjacent to the column sub-pixel electrodes and in immediate contact with the light emitting layer and are connected to at least one of the line patterned row electrodes through conductive vias featured in the insulation layer between the row and column line patterned electrodes.
The electrode assembly may also feature a plurality of column sub-pixel electrodes adjacent to the row sub-pixel electrodes. The row and column sub-pixel electrodes are separated from the line patterned electrodes with a second insulating layer, are in immediate contact with the light emitting layer and are connected to at least one of the line patterned row and column electrodes, respectively, through conductive vias featured in the insulation layers between the different electrodes.
In a specific aspect of the invention, the electroluminescent display device features a plurality of row and column line patterned electrodes, separated by an insulating layer, a plurality of row sub-pixel electrodes adjacent to the column line patterned electrodes and connected through conductive vias to the row line patterned electrodes, a light emitting layer in contact with the sub-pixel and column electrodes, a transparent pixel defined conductive layer in contact with the side of the light emitting layer opposite from the electrodes, and a transparent substrate in conduct with the conductive pixels. The contact between the sub-pixel electrodes and the row line patterned electrodes is facilitated by a plurality of electrically conductive vias, each via extending through the insulating layer.
The electrode assembly may also feature a substrate, a plurality of opaque line patterned row and column electrodes separated by an insulating layer, and a plurality of row sub-pixel electrodes adjacent to the column electrodes. The insulating layer has conductive vias connecting the line patterned row electrodes with the row sub-pixel electrodes.
The electrode assembly may also feature column sub-pixel electrodes adjacent to the row sub-pixel electrodes and in contact with the light emitting layer. A second insulating layer separates the row and column sub-pixel electrodes from the column line patterned electrodes. The row and column sub-pixel electrodes are connected to the row and column line patterned electrodes by conductive row and column vias featured in the first and second insulation layer, respectively. In this case the transparent conductive film layer may be a continuous unpatterned film.
The electrodes may be opaque, high conductivity metals or alloys such as aluminum or chromium or superconductors. The active area of the electroluminescent device may be hermetically sealed with a cover glass allowing exposure of the electrode contacts. The line patterned electrodes may extend to parallel edges of the substrate for electrical contact with the exciting voltages. The column line patterned electrodes may be directed perpendicular to the row line patterned electrodes. The different layers may be formed by chemical vapor deposition, thermal evaporation, electron beam deposition and sputtering. The vias in the insulating layers may be formed by photolithography, laser ablation or masking methods. The light emitting layer may be a thin film and it may consist of organic electroluminescent materials. The substrate may be an opaque or transparent material selected from the group of silicon, ceramics, insulated metals and glass.
In general, in another aspect, the invention features a method of manufacturing an electroluminescent display including the steps of manufacturing an electrode assembly, testing the electrode assembly, depositing a light emitting layer on the electrode assembly, depositing a transparent conductive layer on the light emitting layer and covering and sealing the active area with a glass cover. The manufacturing of the electrode assembly may feature the steps of depositing a plurality of first line patterned conductive metal electrodes on a substrate, depositing a first insulating layer on the fist line patterned electrodes, forming vias in the insulating layer in contact with the electrodes and depositing a plurality of second line patterned electrodes and a plurality of row sub-pixel electrodes on the first insulating layer, wherein the row sub-pixel electrodes contact the first line patterned electrodes through the formed vias.
In another aspect, the invention features a method of making an electroluminescent display by depositing transparent conductive pixels on a transparent substrate followed by the deposition of a light emitting layer. On top of the light emitting layer high conductivity metal line patterned column electrodes are simultaneously deposited with row sub-pixel electrodes. An insulating layer is then deposited over the line patterned column and row sub-pixel layer with conductive vias penetrating through the insulating layer thickness. An electrically conducting material is then deposited defining the line patterned row electrode. The line patterned row electrodes extend to the edges of the substrate for electrical contact and contact the row sub-pixel electrodes through the said vias. A cover glass is then added over the active structure hermetically sealing the device, but allowing exposure of row and column electrodes ends for electrical connection. This method may include depositing column sub-pixel electrodes adjacent to the row sub-pixels and a second insulating layer separating the sub-pixel electrodes form the column line patterned electrodes. The second insulation layer has conductive vias connecting the sub-pixel electrodes to the line patterned electrodes.
In yet another aspect, the invention features a method of making an electroluminescent device by depositing line patterned column electrodes on a substrate of glass, ceramic or insulated metal extending to parallel edges of the substrate for electrical connection. An insulating layer, featuring column vias and row vias, is then added over the column electrodes. Line patterned row electrodes are then deposited at right angles to column electrodes over the insulating layer and extend to parallel edges of the substrate for electrical connection. Another insulating layer is then deposited over the line patterned row electrodes, preserving the column vias and adding row vias. Row and column sub-pixels are now deposited connecting through row and columns vias to appropriate electrodes. A light emitting layer of known design is now added on top of the row and column electrode systems. An unpatterned transparent conductive coating is deposited over and limited to the light emitting layer area. A cover glass acting as hermetic seal is now added over the structure, but allowing for edge connection to the row and column electrodes.
Among the advantages of the invention may be one or more of the following. The electrode assembly of the invention reduces the number and size of electrodes required to achieve high pixel resolution, allows the application of high conductivity opaque metal electrodes, and enables the manufacture of large size displays with reduced power losses. The invention provides the ability to manufacture the entire electrode assembly independent from the electroluminescent portion of the device. This allows for testing of the electrode assembly prior to the deposition of the light emitting layer resulting in higher quality yields and increased production throughput for the electroluminescent display device than currently possible.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and the claims.